In general, the spoke rim wheel for a bicycle comprises an annular rim for holding a tire, a hub located in the center of the rim to hold the rim on a wheel, and spokes for connecting the rim and the hub. The spoke is inserted into a mounting hole bored in a flange portion of the hub. A head of the spoke is placed in engagement with the mounting hole, and an end with a thread tapped is threadedly mounted by a nipple inserted into a through-hole bored in a zigzag manner in a peripheral direction of the rim from the outer side of the rim, that is, from the side on which a tire is put to apply tension to the spoke. Therefore, the through-hole of the rim has no airtightness at all, and, since the head of the nipple and the end of the spoke project on the outer side of the rim, it is impossible to make use of the tubeless tire on the spoke rim wheel.
Some constructions in which a tubeless tire is used are disclosed in Japanese Utility Model Application Laid-Open Nos. S50-134857, S50-134858, and S51-156147 Publications. In these constructions, spoke-mounting tongues are provided over the entire periphery on the inner side of the rim; that is, on the spoke-mounting side, the tongues being bored with spoke-inserting through-holes. However, these constructions are complicated, and besides, since tightening of spokes is done in a special way, the operation for applying tension to the spokes is cumbersome.
On the other hand, other constructions are disclosed in Japanese Utility Model Publication No. S35-29401 Publication and Japanese Utility Model Application Laid-Open No. S48-64903 Publication. In these constructions, airtightness means using a special seal material is employed in order to close through-holes into which spokes are inserted, the holes being bored in a zigzag manner on the outer side of the rim. However, even if these seal materials are used, since the head of the nipple mounted on the rim or the end of the spoke comes in contact with the seal material, the head of the nipple or the end of the spoke pushes up or laterally moves the seal material due to complicated vibrations in all directions received during running, posing an inconvenience that the airtightness fails to hold due to the generation of breakage, deviation, peeling, and the like, of the seal material.
For overcoming such an inconvenience as described above, there is proposed means as disclosed in Japanese Patent Application Laid-Open No. H7-112601. This means is constructed such that a dovetailed tenon groove is provided in a rim, a rubber band is disposed in the groove, a protrusion internally projecting from the rim forms a bead seat of a tire 5, that is, a bead-seating portion, and a tire bead extends internally from the bead-seating portion of the rim so that the bead is partly supported on the upper surface of the rubber band disposed in the groove to press the rubber band so as to maintain the airtightness. The means disclosed in that publication has a construction capable of securing the airtightness. However, since the tire bead is partly supported on the upper surface of the rubber band provided in the groove, the tire bead need be widened. In addition, when the tire is fitted in the rim, the extreme end of the bead required to fit the tire cannot be temporarily moved into the groove because the groove is filled with the rubber band and the tire bead is wide, as described above, thus posing an inconvenience that the tire is difficult to mount on the rim, and the thick rubber band causes the weight of the wheel to increase.
The present invention is to solve the problem as noted above. The invention provides a bicycle spoke rim wheel for a tubeless tire of the wire-on type (so-called "WO Type"), in which airtightness can be maintained positively, the entire wheel can be reduced in weight, and mounting of tire on the rim can be done easily; and further, means is provided in which a seal material within a groove that is, a recess can be reduced in weight, and movement of a tire bead into the recess is enabled.